1. Field of the Invention
The present invention is related to a complex antenna, and more particularly, to a complex antenna which suits both dimension and cost requirements, ensures high antenna gain value and beam coverage rate, and offers adaptive beam alignment capabilities.
2. Description of the Prior Art
Electronic products with wireless communication functionalities utilize antennas to emit and receive radio waves, to transmit or exchange radio signals, so as to access a wireless communication network. With the advance of wireless communication technology, demand for transmission capacity and wireless network ability has grown dramatically in recent years. A long term evolution (LTE) wireless communication system and a wireless local area network standard IEEE 802.11n both support multi-input multi-output (MIMO) communication technology, which can vastly increase system throughput and transmission distance without increasing system bandwidth or total transmission power expenditure, thereby effectively enhancing spectral efficiency and transmission rate for the wireless communication system, as well as improving communication quality. Consequently, MIMO communication technology plays a critical role in a wireless communication system.
There are many kinds of antennas that support MIMO communication technology. A panel-type antenna has less complex structure and is rather inexpensive. However, the beamwidth of the panel-type antenna in the horizontal plane is narrow, meaning that its beam coverage rate is low, and hence the panel-type antenna can hardly be mounted easily and accurately. Worst of all, the panel-type antenna lacks adaptive beam alignment capabilities. With an antenna motor, direction of the panel-type antenna can be changed to find best reception, thereby solving the major drawback of the panel-type antenna. An antenna motor however costs a lot of money and sets limits on installation conditions, which cannot accommodate the trend for smaller-sized electronic products. FIG. 1 is a schematic diagram illustrating a complex antenna 10. The complex antenna 10 disposed in a cylindrical radome RAD comprises antenna units U1, U2, U3 and U4 of identical structure and size. The antenna units U1 to U4 divide the cylindrical radome RAD up into 4 equal sections each having the same space angle; consequently, a projection of the complex antenna 10 orthogonally projected onto a horizontal plane is symmetrical with respect to 4 symmetrical axes. The complex antenna 10 has high beam coverage rate and receives signals from or transmits signals to all directions without being pointed. The complex antenna 10 requires no antenna motor and cuts the cost, but the complex antenna 10 occupies more space. Compared with the area of a reflective unit of the panel-type antenna, the area of a reflective unit of each antenna unit (for example, the antenna unit U1) in the complex antenna 10 is smaller, such that antenna gain value of each antenna unit of the complex antenna 10 would be lower.
Therefore, it is a common goal in the industry to design antennas that suit both dimension and cost requirements, ensure high antenna gain value and beam coverage rate, and offer adaptive beam alignment capabilities.